The present invention relates to the general field of gem faceting apparatus and more specifically to such apparatus utilizing a vertically adjustable faceting head support assembly for elevationally locating the attached gem at a selected elevation relative to a lap surface.
Gem faceting machines are utilized to cut or polish facets in precious or semi-precious stones. Such a machine is disclosed in U.S. Pat. No. 3,815,289 which is also directed toward a gem faceting machine having an adjustable faceting head support assembly. Such faceting machines generally include a powered "lap" or grinding wheel for rotation about a vertical axis in a fixed horizontal place. The gem is held by a "faceting head" including a "dop" elevationally adjacent the lap at one end of a "dop arm". It is generally desirable to angularly and elevationally position the gem relative to the lap surface. This procedure is accomplished by an angle adjusting mechanism associated with the dop arm and an adjustable elevational support for the faceting head. The present invention is concerned primarily with such supports, utilized in conjunction with gem faceting apparatus.
The dop and dop arm are ordinarily positioned by a support yoke and are elevationally positionable by adjustment of a support frame slidably mounted to a vertical support or mast. Fine elevational adjustments are conventionally controlled by a separate adjusting screw assembly provided between the yoke and dop arm. Horizontal pivotal movement of the dop arm is usually centered about the axis of a secondary shaft spaced laterally of the central axis of the supporting mast.
The primary disadvantage of the above described apparatus is that the pivotal movement of the faceting head requires more than one vertical axis. This presents a possibility of compounding several errors within normal tolerance limits. Further, this type of assembly requires that the dop be supported a substantial distance from the support shaft, creating more likelihood that the support shaft will deflect or bend as leverage is applied at the end of the dop arm.
Apparatus disclosed in my prior U.S. Pat. No. 3,815,289 serves to eliminate the disadvantages discussed above. This apparatus utilizes a pivotable rack and gear assembly for precisely positioning the dop arm elevationally relative to a lap surface and for enabling pivotal movement of the dop arm about the axis of the supporting mast. The present invention is comprised of an improved faceting head support wherein the vertical adjustment and pivot arrangement of the dop support mechanism is more simply constructed and eliminates, to a substantial degree, backlash between the faceting head support and vertical adjusting assembly.